Evolutionary relationship between yeast telomeric protein Cdc13 and Pot1

The CST complex protects the ss-overhang of telomeres. In animals, it is composed of CTC1, STN1 and TEN1. In Schizosaccharomyces pombe, CTC1 is absent, while in Saccharomyces cerevisiae it is substituted by Cdc13. Pot1 is the only Shelterin protein that binds ssDNA, and is absent in Saccharomyces cerevisiae. In this study, I looked for homologues of CTC1, Cdc13 and Pot1 in Fungi. I found that CTC1 has been lost in Dikarya (yeasts and mushrooms), with its function probably being taken by Pot1. Furthermore, my analyses show that Cdc13 probably evolved from Pot1, by the loss of its third domain, which is responsible for binding Tpz1. In this way, Est3 (the orthologue of Tpz1 in Saccharomyces cerevisiae) became part of the telomerase complex. Cdc13 further evolved by gene duplication in some budding yeasts, giving rise to two paralogues in Serinales, Ascoideales, Phaffomycetales, Saccharomycetales and Saccharomycodales: in these latter two orders, the two paralogues fused to give rise to a "long" Cdc13. Beyond their evolutionary interest, these results could be useful for researchers using new species of yeasts as model organisms.